1. Field of the Invention
The present invention relates to a technique of controlling operations of a fuel cell system.
2. Description of the Related Art
Fuel cell systems generating electric power by an electrochemical reaction of hydrogen with oxygen have recently drawn attention as the novel energy source. The fuel cell system requires a supply of hydrogen for power generation. The hydrogen to be supplied to the fuel cell system is stored under pressure in a hydrogen tank and is depressurized to a preset pressure level by a pressure regulator, prior to the supply.
A typical example of the pressure regulator to depressurize the pressurized hydrogen is a diaphragm regulator. In the diaphragm regulator disclosed in Japanese Patent Laid-Open Gazette No. 2002-75418, the secondary supply pressure of hydrogen storage in a hydrogen tank is reduced to the atmospheric level by introducing the atmospheric pressure as a reference pressure into a diaphragm chamber.
The atmospheric pressure varies according to the altitude of the location of the fuel cell system and the climate conditions. In the conventional fuel cell system, the pressure of the hydrogen supply flowed out of the pressure regulator may be varied unstably. The varying pressure of the hydrogen supply may interfere with stable output of electric power. Even in the normal operation state of the fuel cell system, the varying pressure of the hydrogen supply may activate a safety device and lead to misjudgment of an abnormal state of the fuel cell system. Such misjudgment may cause significant troubles especially in moving bodies equipped with the fuel cell system, for example, motor vehicles, aircraft, and railway vehicles.